Reflection of an Orienting Reflex in the Phases of Evoked Potentials in the Rabbit Visual Cortex and Hippocampus during Substitution of Stimulus Intensity

Experiments on conscious rabbits were performed using the oddball paradigm, in which a rare (deviant) and common (standard) stimuli were of the same color but different intensities. Deviant stimuli were of lesser intensity. Recordings were made of evoked potentials induced by series of uniform deviant stimuli (without using standard stimuli), which were presented at the beginning and end of stimulation. Visual evoked potentials recorded in response to deviant stimuli in the visual cortex and hippocampus showed increases in the amplitudes of phases, shifted towards positivity as compared with responses to standard stimuli and uniform deviant stimuli at the beginning and end of stimulus blocks. Significant changes affected phases P1 and P2 of visual evoked potentials in the cortex and phases P1, N1, and P2 in the hippocampus. The most significant increase in evoked potentials in the cortex was seen for the P2 peak (P130). It is suggested that changes in responses to oddball-deviant stimuli result from an orienting reflex to rare, unexpected stimuli and that the P2 (P130) peak in the cortex is associated with transmission of information regarding changes in the intensity of the light. The amplitude of this peak was shown to be decreased in responses to uniform deviant stimuli at the beginning and end of stimulus blocks. It was also demonstrated that the clearest and most contrasting changes in visual evoked potentials in responses to deviant and standard stimuli were seen with the smallest differences in intensity between these types of stimulus, this reflecting increases in the orienting reflex at threshold differences.     

Short-Term Habituation and Dishabituation of the Mismatch Negativity of the ERP

Standard tones of 1000 Hz and deviant tones of 1250 Hz were presented in random order, 1 stimulus/second. The probabilities of the standards and deviants were 90% and 10%, respectively. In one condition the subject counted the deviant stimuli and in the other condition he/she read a comic book. ERPs were separately averaged to 1) the standard preceding the deviant, 2) the “first deviant” preceded by at least 4 standards, 3) the “second deviant” (an occasional deviant immediately following the “first deviant”), 4) the first and 5) the second standard following the “first deviant,” 6) the first and 7) the second standard following the “second deviant.” It was found that the mismatch negativity evoked in both conditions by the first deviant was considerably larger than to the second deviant. Also the first standard following the first deviant evoked the mismatch negativity. The results are discussed in terms of parallel neuronal models of the stimuli as reflected by the mismatch negativity.     

An electrophysiological index of stimulus unfamiliarity

This study investigated the functional significance of the N2 response to novel stimuli. In one condition, background, target, and deviant stimuli were simple geometric figures. In a second condition, all stimulus types were unfamiliar/unusual figures. In a third condition, background and target stimuli were unusual figures and deviant stimuli were simple shapes. Unusual figures, whether they were deviant, target, or background stimuli, evoked larger N2 responses than their simple, familiar counterparts. N2 elicited by an unusual background stimulus was larger than that evoked by simple, deviant stimuli, a pattern opposite that exhibited by the subsequent P3. Deviance from immediate context had limited influence over N2 amplitude. The results suggest that novelty N2 and novelty P3 reflect the processing of different aspects of "novel" visual stimuli. The novelty P3 is particularly sensitive to deviation from immediate context. In contrast, the novelty N2 is sensitive to deviation from long-term context that renders a stimulus unfamiliar and difficult to encode.     

Active attention modulates passive attention-related neural responses to sudden somatosensory input against a silent background

To reveal whether active attention modulates neuronal responses related to passive attention to somatosensory stimuli presented suddenly against a silent background, we examined the passive attention-related change in amplitude of the event-related brain potentials (ERPs), caused by temporal infrequency of stimuli. Eighteen healthy subjects performed passive and active attention tasks in two stimulus conditions. In the oddball condition, frequent (80%, standard) and infrequent (20%, deviant) electrical stimuli were randomly delivered to the second and third digits of the left hand. In the deviant-alone condition, the deviant stimulus (deviant-alone stimulus) was delivered with the same timing and sequence as in the oddball condition without standard stimuli. The P100, N140, and P200 elicited by the deviant-alone stimulus were enhanced in amplitude compared to those evoked by the oddball deviant stimulus in both the active and passive tasks. Moreover, active attention increased the enhancement of P100 and N140. The difference waveform (deviant-alone minus oddball deviant) provided similar findings. In conclusion, active attention enhances neural responses related to passive shifts of attention to somatosensory signals suddenly presented against a silent background. The results indicate that top-down signals for detecting target stimuli interact with passive shifts of attention caused by bottom-up signals.     

Discrimination of emotional facial expressions in a visual oddball task: an ERP study

Several ERP studies have shown an orienting complex, the N2/P3a, associated to the detection of stimulus novelty. Its role consists in preparing the organism to process and react to biologically prepotent stimuli. Whether this N2/P3a: (1) could be obtained with complex visual stimuli, such as with emotional facial expressions; and (2) could take part in a complex discrimination process has yet to be determined. To investigate this issue, event-related potentials were recorded in response to repetitions of a particular facial expression (e.g. sadness) and in response to two different deviant (rare) stimuli, one depicting the same emotion as the frequent stimulus, while the other depicted a different facial expression (e.g. fear). As expected, deviant stimuli evoked an N2/P3a complex of larger amplitude than frequent stimuli. But more interestingly, when the deviant stimulus depicted the same emotion as the frequent stimulus the N2/P3a was delayed compared to the response elicited by the different-emotion deviant. The N2/P3a was thus implicated in the detection of physical facial changes, with a higher sensitivity to changes related to a new different emotional content, perhaps leading to faster adaptive reactions.     

An alternative baseline measure for calculation of the mismatch negativity (MMN) component of the event-related potential (ERP).

Mismatch negativity (MMN), a component of the event-related potential, reflects the processing associated with low-probability (deviant) stimuli over and above that required for high-probability (standard) stimuli. Occurring 100-250 ms post stimulus, MMN is evident in the enhanced negativity generated in response to deviant relative to standard stimuli. Traditionally, the MMN waveform is calculated by subtracting the averaged waveform of all standard stimuli from the averaged waveform of all deviant stimuli collected during the same test session. To investigate whether an unbroken, extended string of standard stimuli may minimize baseline processing, thereby resulting in a more robust measure of MMN, 11 participants were exposed to two contiguous blocks of 1000 trials, each beginning with 60 uninterrupted standard stimuli followed by 940 randomized standard and deviant trials. Negativity related to standard stimuli was minimized in the average of uninterrupted standard stimuli from the second block of trials only while negativity related to uninterrupted standards in the first block of trials was increased relative to all other conditions. The present findings suggest that a familiar, uninterrupted string of standard stimuli, presented midway through an experimental session, may provide a useful alternative baseline for the calculation of MMN.     

The duration of a neuronal trace of an auditory stimulus as indicated by event-related potentials

Event-related brain potential studies have revealed a component called the mismatch negativity (MMN) in response to occasional deviant stimuli presented in a sequence of homogeneous repetitive, ‘standard’, stimuli. This negativity probably reflects an automatic neuronal-mismatch process with a neuronal representation of the standard stimulus. The present study aimed at determining the duration of the assumed neuronal representation by varying the inter-stimulus interval (ISI) of a stimulus block. It was assumed that a deviant stimulus can elicit a MMN only when the neuronal representation of the previous standard stimulus still exists. It was found that a clear MMN was elicited by the deviant stimulus when the ISI was 1 or 2 s, but not when the ISI was 4 or 8 s. This suggests that the duration of the neuronal representation involved was less than 4 s.     

Parietal P3 Response as an Indicator of Stimulus Categorization: Increased P3 Amplitude to Categorically Deviant Target and Nontarget Stimuli

Two experiments were performed in which we compared the effects of selected non-deviant versus categorically deviant stimuli on parietal P3 under a variety of conditions in which one, both, or neither stimulus was a target of an experimental task. Subjects were repeatedly presented with series of 8 numeric stimuli and 1 alphabetic (Deviant) stimulus. P3 amplitudes to target and nontarget Deviant stimuli were consistently and significantly larger than to other, non-deviant targets and nontargets, respectively. Nontarget Deviant stimuli evoked P3 amplitudes comparable to those evoked by low-probability non-deviant targets. The observed differences indicate that P3 amplitude is a sensitive indicator of perceived category differences, and that the effect of category deviance on parietal P3 amplitude is independent of task response classification (target or nontarget) and of response probability.     

The effect of stimulus probability on the somatosensory mismatch field

We investigated the effect of deviant stimulus probability on the somatosensory magnetic mismatch negativity (MMNm) using an electrical two-point stimulation. First, we determined the discrimination threshold (DT) of the two-point distance. We applied standard stimuli at a distance that subjects felt as one point and deviant stimuli at a distance that subjects definitely felt as two points. We used three deviant stimulus probabilities, 10, 30, and 50%. The components peaking around 30–70 ms (first component) and 150–250 ms (fourth component) following deviant stimuli were significantly larger than those following standard stimuli in 10% condition, but not in 30 or 50% condition. The equivalent current dipole (ECD) was located in the contralateral primary somatosensory cortex (cSI) for the first component, and in the cSI and in the contralateral secondary somatosensory cortex (cSII) for the fourth component. The peak amplitude of the MMNm decreased as the probability of the deviant stimulus increased. The Somatosensory MMNm was affected by deviant stimulus probability similar to an auditory mismatch negativity (MMN).     

Finding the missing stimulus mismatch negativity (MMN): emitted MMN to violations of an auditory gestalt

Deviations from repetitive auditory stimuli evoke a mismatch negativity (MMN). Counterintuitively, omissions of repetitive stimuli do not. Violations of patterns reflecting complex rules also evoke MMN. To detect a MMN to missing stimuli, we developed an auditory gestalt task using one stimulus. Groups of six pips (50 ms duration, 330 ms stimulus onset asynchrony [SOA], 400 trials), were presented with an intertrial interval (ITI) of 750 ms while subjects (n=16) watched a silent video. Occasional deviant groups had missing 4th or 6th tones (50 trials each). Missing stimuli evoked a MMN (p<.05). The missing 4th (-0.8 μV, p<.01) and the missing 6th stimuli (-1.1 μV, p<.05) were more negative than standard 6th stimuli (0.3 μV). MMN can be elicited by a missing stimulus at long SOAs by violation of a gestalt grouping rule. Patterned stimuli appear more sensitive to omissions and ITI than homogenous streams.     

Gender differences in behavioral inhibitory control: ERP evidence from a two-choice oddball task

The inhibition of inappropriate behaviors is important for adaptive living in changing environments. The present study investigated gender-related behavioral inhibitory control by recording event-related potentials for standard and deviant stimuli while subjects performed a standard/deviant distinction task by accurately pressing different keys within 1000 ms. The results showed faster reaction times (RTs) for deviant stimuli in women than in men, although RTs for standard stimuli were similar across genders. There were significant gender and stimulus interaction effects on mean amplitudes during each of the 170–230-ms, 250–330-ms, and 350–600-ms intervals, and women exhibited shorter latencies and larger amplitudes than men at deviant-related P2, N2, and P3 components. As an accurate, fast response to the rare deviant stimuli involves behavioral inhibitory control on the prepotent response whereas the response to the standard stimuli does not, it is clear that there is a general gender difference in behavioral control for human adults. This may relate to differential inhibitory demands by each gender during evolution.     

Effects of the Azimuthal Position of Stationary and Moving Sound Images on the Mismatch Negativity Phenomenon

This report presents results obtained from studies of the phenomenon of mismatch negativity in conditions of dichotic stimulation with presentation of deviant stimuli modeling movement of a sound image towards or away from a standard stimulus and on presentation of stationary deviants located at an angle of 90° to the standard. Standard stimuli were located close to the left or right ear or in the midline of the head. All deviant stimuli induced mismatch negativity. Movement of the deviant stimulus from the standard was found to induce mismatch negativity with the longest latency and smallest amplitude for all azimuthal positions of the standard stimulus. In addition, it was only in this direction of movement that there was a relationship between measures of mismatch negativity and the azimuth of the standard. It was suggested that the process of the recognition of differences between interaural delay times is significantly dependent on the nature of changes in this parameter at the moment at which the deviant stimulus is presented.__________Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 90, No. 9, pp. 1081–1093, September, 2004.     

A Visual Analog of Mismatch Negativity When Stimuli Differ in Duration

Event-linked brain potentials were studied in ten essentially healthy volunteers (six men, four women) aged 18–24 years. Subjects were presented with rare deviant and frequent standard visual stimuli in the standard odd-ball paradigm in conditions of active attention to stimulation and in conditions of distracted attention. Differences between deviant stimuli (50, 100, and 150 msec) and standard (200 msec) stimuli ranged from 50 to 150 msec. Negative difference waves (deviant stimulus with distracted attention minus control stimulus of the same duration) were seen at differences of 100 and 150 msec and these were most marked in the right temporal cortex 200–400 msec from stimulus onset. As this wave was seen in conditions of distracted attention, it appears to be a visual analog of mismatch negativity and reflects the process of the automatic detection of stimuli with deviant durations.     

Mechanisms of Generation of Mismatch Negativity and Their Role in the Recognition of Brief Auditory Stimuli

The endogenous components of auditory evoked potentials were studied in the human brain, arising in conditions of voluntary and involuntary attention. Variation of the duration of acoustic stimuli led to a situation in which the generation of mismatch negativity was blocked. The recognition of acoustic stimuli was compared in conditions in which passive perception of the deviant signal in some cases evoked mismatch negativity and in others did not. This demonstrated the following: 1) stimuli not evoking mismatch negativity in the classical oddball paradigm can be recognized efficiently; 2) recognition of stimuli evoking mismatch negativity (in conditions of passive perception) occurs with a significantly shorter response time. The difference in the present experiments was 49–51 msec. There was also an increase in the proportion of correct responses to the deviant stimulus (to 92%). Thus, if the experimental conditions allow the mechanism generating mismatch negativity to trigger, then the response time to the actively perceived stimulus decreases. These results are evidence that the mechanisms of involuntary attention contribute to the active perception of acoustic stimuli.     

ERPs for infrequent omissions and inclusions of stimulus elements

A negative event-related potential (ERP) wave called mismatch negativity (MMN) is elicited by an infrequent deviant stimulus in a sequence of frequent standard stimuli. Omission of a stimulus in a sequence of stimuli, however, has been considered to elicit a negativity different from MMN. The present study addressed this issue by examining ERPs for infrequent omissions and inclusions of compound stimuli or their elements. Three kinds of stimuli were presented: a 1000-Hz sine wave tone (Sine), white noise with the 1000-Hz frequency sharply filtered out (Noise), and a composite of the pure tone and the filtered white noise (SiNoise). All stimuli had 50 ms duration and were presented with a regular interstimulus interval of 650 ms. Intensities were 75 dB SPL for the tone and noise stimuli and slightly higher for the composite stimulus. The three kinds of stimuli were presented on separate runs, either as the frequent stimulus or one of two infrequent stimuli, each with 10% probability. Infrequent omission of the large stimulus element (Sine deviant to SiNoise) tended to elicit later MMN than inclusion of the same element (SiNoise deviant to Sine). Omission of the small stimulus element (Noise deviant to SiNoise) elicited a smaller and later MMN than did inclusion of the same element (SiNoise deviant to Noise). These data suggest that MMNs are also elicited by partial stimulus omissions, although they seem to be more sensitive to other kinds of stimulus deviances.     

The combined perception of emotion from voice and face: early interaction revealed by human electric brain responses

Judgement of the emotional tone of a spoken utterance is influenced by a simultaneously presented face expression. The time course of this integration was investigated by measuring the mismatch negativity (MMN). In one condition, the standard stimulus was an angry voice fragment combined with a (congruous) angry face expression. In the deviant pair, the voice expression was kept the same and only the face expression changed to an (incongruous) sad face. The pairs with a deviant visual item evoked a negative electric brain response showing the characteristics of the MMN, which is usually evoked only by auditory deviations. Similar results were obtained by employing incongruous standard and congruous deviant pairs. These findings provide compelling evidence of an early integration of face with voice information in the processing of affect.     

The effect of stimulus expectancy on dishabituation of auditory evoked potentials

ObjectivesHaving foreknowledge of the type and timing of sensory stimulation modulates the electrophysiological response and can result in short-term habituation. Here we explore if dishabituation is similarly affected.MethodsSeventeen healthy subjects were tested with five different auditory stimuli paradigms to see if knowledge of the stimulus train length and/or deviant stimulus affects the amount of dishabituation of auditory evoked potentials. Furthermore it was determined if the degree of difference between the repeating stimulus and deviant stimulus affected the amount of dishabituation.ResultsStimulus complexity is the main determinant of the degree of dishabituation, followed by lack of knowledge about train length. Not knowing the deviant stimulus has little or no effect on dishabituation. Also, P200 is the most affected by expectancy and P50 not at all.ConclusionsForeknowledge of the type and timing of sensory stimulation modulates the degree of dishabituation.SignificancePrevious reports have shown that expectancy does affect (certain) evoked potential components. Here we extend this knowledge to the effect of expectancy on dishabituation.     

Neural generators of the auditory evoked potential components P3a and P3b

The aim of the present study was to define the scalp topography of the two subcomponents of the P3 component of the auditory evoked potential elicited in a three-stimulus oddball paradigm and to identify their cortical generators using the standardized low resolution electromagnetic tomography (sLORETA). Subjects were presented with a random sequence of auditory stimuli and instructed to respond to an infrequently occurring target stimulus inserted into a sequence of frequent standard and rare non-target stimuli. Results show that the magnitude of the frontal P3a is determined by the relative physical difference among stimuli, as it was larger for the stimulus more deviant from the standard. Major neural generators of the P3a were localized within frontal cortex and anterior cingulate gyrus. In contrast to this, the P3b, showing maximal amplitude at parietal locations, was larger for stimuli demanding a response than for the rare non-target. Major sources of the P3b included the superior parietal lobule and the posterior part of the cingulate gyrus. Our findings are in line with the hypothesis that P3a is related to alerting activity during the initial allocation of attention, while P3b is related to activation of a posterior network when the neuronal model of perceived stimulation is compared with the attentional trace.     

Arousal and valence effects on event-related P3a and P3b during emotional categorization

Due to the adaptive value of emotional situations, categorizing along the valence dimension may be supported by critical brain functions. The present study examined emotion–cognition relationships by focusing on the influence of an emotional categorization task on the cognitive processing induced by an oddball-like paradigm. Event-related potentials (ERPs) were recorded from subjects explicitly asked to categorize along the valence dimension (unpleasant, neutral or pleasant) deviant target pictures embedded in a train of standard stimuli. Late positivities evoked in response to the target pictures were decomposed into a P3a and a P3b and topographical differences were observed according to the valence content of the stimuli. P3a showed enhanced amplitudes at posterior sites in response to unpleasant pictures as compared to both neutral and pleasant pictures. This effect is interpreted as a negativity bias related to attentional processing. The P3b component was sensitive to the arousal value of the stimulation, with higher amplitudes at several posterior sites for both types of emotional pictures. Moreover, unpleasant pictures evoked smaller amplitudes than pleasant ones at fronto-central sites. Thus, the context updating process may be differentially modulated by the affective arousal and valence of the stimulus. The present study supports the assumption that, during an emotional categorization, the emotional content of the stimulus may modulate the reorientation of attention and the subsequent updating process in a specific way.     

The valence strength of unpleasant emotion modulates brain processing of behavioral inhibitory control: neural correlates

As an ability critical for adaptive social living, behavioral inhibitory control (BIC) is known to be influenced substantially by unpleasant emotion. Nevertheless, how unpleasant emotion of diverse strength influences this control, and the spatiotemporal dynamics underlying this influence, remain undetermined. For this purpose, Event-related potentials (ERPs) were recorded for standard stimulus which required no BIC, and for deviant stimuli that required controlling habitual responses, during highly unpleasant (HU), mildly unpleasant (MU) and Neutral blocks. The results showed delayed response latencies for deviant compared to standard stimuli, irrespective of emotionality. Moreover, there were significant main effects of stimulus type, and significant stimulus type and block interaction effects on the averaged amplitudes of the 230-310 ms and 330-430 ms intervals. In the deviant-standard difference waves which directly index BIC-relevant processing, these interactions were manifested by increased negative potentials as a function of the strength of unpleasant emotion across N2 and P3 components. In addition, these influences are specific to unpleasant emotion, as pleasant emotion of diverse strength produced a similar impact in the control experiment. Therefore, unpleasant emotion of diverse strength is different in impact on brain processing of behavioral inhibitory control. This impact is evident not only in early monitoring of response conflicts, but also in late processing of response inhibition.